This invention relates to a bumper of an automobile, and particularly to a bumper beam for reinforcing the bumper made of a resin.
The resin bumper has a plan view that at both ends of an center portion extending in a car width direction over the almost entire width are formed corner portions bent toward car body side so as to extend along side surfaces of the car body, and is shaped like a box opened toward the car body side. Therefore, the bumper beam to be extended along the bumper is also formed in the similar shape.
The bumper beam is manufactured by forming a metal plate. In the case that it is intended to reduce the weight of the bumper beam by using a high-tensile steel having a specially high tensile strength of 120 kgf/mm.sup.2 class for example as the metal plate, it is very difficult to form the pumper beam having the above-mentioned shape by a drawing process together with the corner portion.
Hitherto, in such a case, the bumper beam (reinforce) was divided into a straight central portion having a U-shaped section (reinforce main body) and two corner portions (reinforce sides) of both ends and after the portions were formed independently of each other, the corner portions were welded to both ends of the central portion to construct the bumper beam, as shown in Japanese Patent Publication No. Hei 4-24259 and Japanese Patent Publication No. Hei 2-19328, for example.
Even in this case, it was common that only the central portion having a relatively simple shape was formed by bending of a high-tensile steel plate of 120 kgf/mm.sup.2 class for example, and the corner portions having complicated shapes was formed by drawing of a relatively mild high-tensile steel plate of 60 kgf/mm.sup.2 for example.
However, in the bumper beam constructed by welding the central portion and the corner portions which are formed as separate parts to each other as described above, many welding man-hour is required, material yield rate is poor and the cost rises because respective different dies are necessary for forming the central portion and the corner portions.